I ASSUMED that my 30x, with 2GB card installed, MapInstall would show 5.8 GB of memory. It didn't. OK, my bad for assuming. I figured out that memory cards now showing up as a separate USB drive. But I didn't learn that from the owner's manual.
Since my original question was whether a better owner's manual were available, it would have been much more helpful if the above replies had said something like, "Check out the tutorials on this site. They may have what you are looking for."
I've since found other sites with more detailed Garmin guidance, but a little pointing in the right direction would have been more helpful than picking apart my posts on such things as whether the memory MapInstall showed on my Hcx included internal memory on the Hcx or just the SD card.